const normalizeDate = (input) =>
  typeof input?.toDate === "function" ? input.toDate() : new Date(input);

const buildMonthKey = (timestamp) => {
  const date = normalizeDate(timestamp);
  const year = date.getUTCFullYear();
  const month = String(date.getUTCMonth() + 1).padStart(2, "0");
  return `${year}-${month}`;
};

const buildPreviousMonthContext = (referenceDate) => {
  const current = referenceDate ? new Date(referenceDate) : new Date();
  current.setUTCHours(0, 0, 0, 0);
  current.setUTCDate(1);

  const target = new Date(current);
  target.setUTCMonth(target.getUTCMonth() - 1);

  const year = target.getUTCFullYear();
  const monthIndex = target.getUTCMonth();
  const rangeStart = new Date(Date.UTC(year, monthIndex, 1, 0, 0, 0, 0));
  const rangeEnd = new Date(Date.UTC(year, monthIndex + 1, 0, 23, 59, 59, 999));
  const monthKey = buildMonthKey(rangeStart);

  return {
    year,
    month: monthIndex + 1,
    monthKey,
    rangeStart,
    rangeEnd,
  };
};

module.exports = {
  buildMonthKey,
  buildPreviousMonthContext,
};